ESTRO 2024 - Abstract Book

S374

Beachytherapy - Physics

ESTRO 2024

1. Obtaining the coordinates: at the end of planning, the TPS (HDRplus 3.0®) issues a report, from which Cartesian coordinates of all the points of interest and stop times are obtained in .CSV format, which are subsequently compiled when executing the developed program. 2. Dose calculation at each point: The dose contribution at each stop must be calculated for each point of interest represented by polar coordinates. To do this, the Cartesian coordinate data obtained previously are converted to polar coordinates (r, θ) in order to be used in the TG43 formula defined as:

In addition to calculating the dose contribution of each source, the value obtained must be corrected for the attenuation of the applicator. Finally, by adding up the contribution of the dose delivered at each source stop, the total dose delivered at each point of interest is obtained.

3. Calculation of differences with TPS report: the relative difference between the dose delivered by our program and that of the TPS is calculated:

International recommendations establish that this difference must be less than 15% (4), otherwise planning must be reviewed before commencing treatment.

Results:

To conduct validation, a retrospective analysis was performed from a sample composed of gynecological cancer patients treated at our brachytherapy center between December 09, 2022 and July 28, 2023. Approval by an ethics committee was obtained, and the protocol was registered with health authorities (Ministry of Public Health no. 8652578). A total of 78 patient records were included, and 3997 calculations were reviewed in 312 brachytherapy insertions. Statistically, the differences recorded between the TPS and the developed software were the following: